Sleep apnea generally refers to the cessation of breathing during sleep. One type of sleep apnea, referred to as obstructive sleep apnea (OSA), is characterized by repetitive pauses in breathing during sleep due to the obstruction and/or collapse of the upper airway, and is usually accompanied by a reduction in blood oxygenation saturation.
One treatment for obstructive sleep apnea has included the delivery of electrical stimulation to the hypoglossal nerve, located in the neck region under the chin. Such stimulation therapy activates the upper airway muscles to maintain upper airway patency. In treatment of sleep apnea, increased respiratory effort resulting from the difficulty in breathing through an obstructed airway is avoided by synchronized stimulation of an upper airway muscle or muscle group that holds the airway open during the inspiratory phase of breathing. For example, the genioglossus muscle is stimulated during treatment of sleep apnea by a cuff electrode place around the hypoglossal nerve.
Because of the significant amount of movement in multiple directions that can take place under the chin, positioning an electrode to enable stimulation of the hypoglossal nerve becomes a significant challenge. On the one hand, placement of the electrode and lead in close proximity to the hypoglossal nerve can result in irritation to the nerve as a result of normal motion of the chin and neck, while on the other hand, without close adherence to the nerve, buildup of connective tissue between the nerve and the electrode cuff and lead can occur, causing low thresholds, thereby reducing the effectiveness of the delivered stimulation by the device.
Another challenge in placing an electrode for nerve stimulation therapy relates to the tendency of the hypoglossal nerve to swell because the nerve is disturbed while manipulating the nerve to implant the cuff electrode and/or while securing the cuff electrode about the nerve. Once the cuff electrode secured on the nerve, swelling of the nerve can result in excess pressure on the nerve by the electrode and lead. In addition, once the electrode has initially been implanted, fibrosis tends to cause the location of the electrode to become more fixed. Therefore, during the first month following the implant of the lead and electrode, it is desirable to keep the electrode cuff properly positioned on the nerve, while at the same time not placing undue pressure on a swelling nerve. An additional challenge in placing the electrode for nerve stimulation results from the fact that stimulation currents should be confined to the hypoglossal nerve in order to prevent other nearby nerves or muscles from being stimulated, which would result in patient discomfort and loss of sleep.